In particular, in navigation systems for motor vehicles having digital maps, databases are used which contain, for example, destination information as data records. In navigation systems, for example, different geographic objects which are selectable by a user are stored as data records of this type, the user entering input data records for this purpose to filter out or select the data records of interest to him from the set of data records.
In the case of navigation systems, it is particularly important for the user to enter information items as input data records for the purpose of having one or more matching destination data records output, thereby making it possible to select an intended destination. This function of navigation systems is typically implemented by using a directory or multiple directories. A directory is a secondary data structure whose purpose is to speed up access to other primary data structures in the same database. There are a number of options for generating directories of this type, for example a tree structure.
One example of a directory is the “point of interest” directory in navigation systems, which is a name directory for such “points of interest” (POI). Databases of navigation systems may contain millions of these points of interest as data records. It is therefore advantageous for the user to quickly select the point of interest he is looking for from the large number of stored points of interest. This can be done by searching all database contents on the basis of the input data entered by the user. However, this takes a relatively long time, which means that this method is not expedient for the user. The POI data in current navigation systems are therefore additionally contained in a global name directory which links at least some names to the points of interest which have these names.
In today's navigation systems, data records, such as points of interest in a region or a country, are searched using a search criterion. A search criterion of this type is, for example, the name. The names of all data records are therefore stored in a directory having a tree structure. However, the ability to additionally filter the data records with regard to other filter criteria, for example according to a “point of interest” category (POI category), would be desirable. For this purpose, however, another tree structure would be needed for the other filter criterion, which, however, would mean that a global search of all data records would no longer be possible within an acceptable amount of time, since all tree structures would have to be combined.